Apparatus for the continuous casting of hollow concrete bodies



Sept. 29, R. F- MAST APPARATUS FOR THE CONTINUOUS CASTING 0F HOLLOW CONCRETE BODIES Filed July 2, 1962 4 Sheets-Sheet 1 "s .QLI we His? 8a? .m, @i a:

INVENTOR.

ROBERT F. MAST R. F'. MAST Sept. 29, 1964 APPARATUS FOR THE CONTINUOUS CASTING OF HOLLOW CONCRETE BODIES 4 Sheets-Sheet 2 Filed July 2, 1962 INVENTOR.

ROBERT F. MAST ATTERIVEYS.

1 1964 R. F. MAST 3,150,428

APPARATUS FOR THE commuous CASTING OF HOLLOW CONCRETE BODIES Filed July 2, 1962 4 Sheets-Sheet 3 I!) IFHtEnuHH AT OR/VEYS.

Sept. 29, 1964 R. F. MAS-T 3,150,423,

APPARATUS FOR THE CONTINUOUS CASTING 0F HOLLOW CONCRETE BODIES Filed July 2, 1962 4 Sheets-Sheet 4 FPr INVENTOR.

ROBERT F. MAST United States Patent APPARATUd FOR THE CQNTINUQUS @ASTKNG 0F HQLLGW COPRCRETE BGDES Robert F. Mast, Tacoma, Wash, assignor to Qonerete Technoicgy Corporation, Tacoma, Wash, 21 corporationof Washington Filed July 2, 1962', Ser. No. 206,750

In iiiairns. (Cl. 25-30) The invention relates to the production of hollow concrete bodies such as pipe or pilings, and more particularly to apparatus for producing such bodies in reinforced concrete.

Several problems are encountered in the casting of large hollow concrete bodies. If the inner form is to remain permanently in the product, economy dictates that such form be of light construction. In large sections, it becomes difiicult to hold a lightly-constructed form accurately in position; furthermore, the construction of a form strong enough to Withstand the concrete pressure becomes quite costly. Many difiiculties in concrete Work have been caused by an inner form collapsing, or floating out of position. If a removable inner form is used, it must be collapsed to be removed, and high labor costs result from the disassembly and reassembly required each time the form is used. Both expendable and removable inner forms are normally positioned before the reinforcing or prestressing steel is placed around them. Thus, a difficulty is encountered in properly positioning the steel in making thin walled bodies, since there is little room to work in the space between inner and outer forms.

Because of these problems encountered with the use of either expendable or collapsible forms, other systems of casting have been devised. However, it seems that such alternate systems create other difiiculties which in some respects can prove to be more serious than the problems discussed above. Thus according to one proposal a hollow pile would be cast section by section with the use of a sharply tapered inner form which is moved after completion of each section. This can only produce a body having a stepped uneven interior surface and which is not truly monolithic by reason of the interval between the casting of successive sections.

According to another proposal, a rotary mandrel and a partial outer form are supported from an overhead railway and moved together over a form which shapes only the lower outside surfaces of a pipe. The part of the outer form supported from the overhead railway, being movable during casting, creates a drag over the cast concrete. Also, such an arrangement interferes with the use of spiral reinforcing in the casting of reinforced concrete piles. Other systems involve the use of cumbersome vertical mold structures. Still others involve centrifuging in rapidly rotating molds which, while feasible in the casting of relatively small concrete bodies, are quite impractical for making large piles and other structures of prestressed concrete.

Slip forming has been used for some time in the construction of vertical structures-particularly chimneys and grain elevators. The forms are jacked upward quite slowly (normally 1 ft./hour or slower) and the concrete is fully set by the time the form clears the concrete. This causes considerable drag on the forms, but, due to the slow rate of motion, it is practical to develop'large forces by means of jacks to move the forms. Furthermore, the weight of the liquid concrete above prevents the solid concrete from adhering to the form. and moving upward with it. If this same basic method is attempted in a horizontal casting scheme, and the speed is increased to be compatible with factory mass production techniques, the following difficulties are encountered: The form must be much longer, due to the increased ice speed of motion, and the drag on the form becomes unmanageable. The hardened concrete adheres to the form, and, without gravity restraining it, it tends to move with the form, often producing severe cracks in the finished product. 7

Another method which involves a moving form is the so-called extrusion process. In this process, both the inside and the outside of a member are formed by a moving machine. This machine is sealed across the front, and the concrete is forced out an aperture in the rear by fiuid pressure. The concrete leaves the machine in a plastic state. While the cohesion of a stiff mix is sufficient to keep the concrete from collapsing in small members, in large members, the concrete must be partially set before the mandrel can be withdrawn. My early experiments showed that the concrete adhered to the mandrel during setting and was dragged forward with it, leaving large cracks in the member. When the mandrel was pulled faster so that the concrete would not have time to set and adhere to the mandrel, the concrete collapsed behind the mandrel. Pre-lubrication of the mandrel, as is common with stationary forms, did not help, since the lubricant was wiped off in the first few yards of travel.

It has been an object of my invention to overcome these and other diiiiculties experienced with known apparatus and techniques as applied to the continuous casting of large reinforced concrete bodies of hollow form.

In seeking such a solution or" the old problems in this art, I have discovered not only how to alleviate the recognized difliculties but also'how some of those difficulties can even be turned to adavntage. Thus, whereas certain prior art procedures were poorly adapted for use where spiral reiniorcementwires are required, I have devised a form of apparatus which can only be benefited by the presence of spiral reinforcing.

My apparatus comprises, in its general arrangement, a floating mandrel which moves continuously through a stationary horizontal outer form and is guided by holddown means projecting downardly through portions of the stationary mold surfaces of the outer form and engaging upper portions of the mold surfaces of the moving mandrel. The mandrel is free to float under hydrostatic pressure of the concrete mix to maintain contact with the hold-down means until the concrete has set sufficiently to maintain a predetermined spacing between the mandrel and outer form. Then the hold-down means can be withdrawn to permit concrete mix to fill the spaces temporarily occupied by the hold-down means.

According to another aspect of my invention, means are provided for selectively applying vibratory forces to forward portions of the moving mandrel to produce a lubricating film of cement and water at the mold surfaces of the mandrel. I have found that this lubricating film has a special value from the standpoint of assisting in free sliding movement of such surfaces without disturbance of the setting concrete and without pulling such surfaces bodily away from the concrete.

These and other features and advantages of my invention will appear more fully from the ensuring description of the best mode contemplated by me for carrying out my invention.

FIG. 1 is a simplified side elevational view of my preferred form of apparatus as adapted for the casting of reinforced concrete piling. This view is in two parts, the lower part being a continuation of the upper part, as indicated by the dot-dash line which connects the common horizontal center line of the two parts. The mandrel is shown in the position which it occupies just before it enters the mold at the beginning of a casting operation.

FIG. la is a diagrammatic representation of a series of related sections of the mandrel of FIG. 1.

FIG. 2 is a vertical longitudinal sectional view of the entering end of the outer form showing the leading end of the mandrel (in elevation) as it enters the outer form during the initial part of the casting operation.

FIG. 3 is a perspective view of the leading end of the mandrel.

FIG. 4- is a perspective view of one complete mandrel section partly broken away in cross section to reveal the interior construction.

FIG. 5 is a perspective view of a portion of the outer form. In this view the upper and lower halves of the outer form are exploded into slightly spaced relationship.

FIG. 6 is an enlarged vertical cross sectional view taken as indicated at 6--6 in FIG. 2.

FIG. 7 is a detail top view of the hold-down means associated with the outer form.

FIG. 8 is a side elevational view of the hold-down means, partly in vertical section.

FIG. 9 is a detail perspective view of the side guide means associated with the outer form, showing the manner of inserting the guide.

FIG. 10 is a view similar to FIG. 9 showing one of the side guides locked in its inserted position.

H6. 11 is a similar view in which the side guide has been removed and has been replaced by a sealing dummy.

FIG. 12 is a detail sectional view taken as indicated at 12-12 in H6. 5.

FIG. 13 is a detail longitudinal sectional view showing the bulkhead structure at the ends of the outer form and also intermediate the ends of such form.

FIG. 14 is a perspective view of a jacking end frame illustrating how the mandrel can be withdrawn through an open central area of said frame prior to final setting of the portion of the piling which is cast last and while the reinforcing strands are still held under the prestressing imposed by the jacking grips.

FIG. 15 is a vertical longitudinal sectional view of a completed section of reinforced piling showing the spiral reinforcing.

Floating Mandrel Structure As applied to the continuous casting of hollow reinforced concrete bodies, my apparatus comprises a horizontal prestressing bed It, means for anchoring reinforcing members 2 to the ends of the bed in positions to extend through wall portions of the cast body, such anchoring means including abutments 3, 4 and associated jacking means one of which is shown at 5 in FIG. 1; and further comprises a horizontal outer form 6 having stationary mold surfaces adapted to form substantially the complete exterior of the cast body, a mandrel 7 movable lengthwise through the outer form and having mold surfaces to form the interior of the body while the mandrel is in continuous movement through the outer form, means for producing such continuous movement of the mandrel, such as the power driven winch a; and cable purchase 9, means for introducing the concrete mix through an upper portion of the outer form during continuous movement of the mandrel, including a hopper 10 suspended from a traveling gantry (not shown) for movement lengthwise of the outer form 6 to selectively discharge the concrete mix through a substantially continuous opening 11 (FIG. 5) extending longitudinally along the upper portion of the outer form 6; and further comprises hold-down means 12 (see especially FIGS. 6, 7 and 8) projecting downwardly through or below upper portions of the stationary mold surfaces of the outer form for engagement with upper portions 13 of the mold surfaces of the moving mandrel. In the particular embodiment illustrated, the mandrel contacting portions of the hold-down means conveniently extend through the opening 11 in the upper portion of the outer form.

With this construction the mandrel is free to float under hydrostatic pressure of the concrete mix to maintain guiding contact with the hold-down means 12 until the concrete has set sufliciently to maintain a predetermined spacing between the mandrel and outer form in accordance with the predetermined position of the mandrel engaging portions 14 of the hold-down means.

In my preferred construction guide means 15 (FIG. 6) project inwardly through side portions of the stationary mold surfaces of the outer form. Such guide means 15 are advantageously located slightly below the center line of the form so that they will not interfere with the free floating action of the mandrel in aligning itself in accordance with the predetermined setting of the holddown means 12.

Also included in my preferred constructions are ballasting means such as provided by bar weights to which serve to maintain an upright position of the floating mandrel, thereby to prevent rotation of the mandrel during its continuous movement through the outer form. Disposition of this ballasting means is shown in FIGS. 1 and 6 to be in the lower part of the mandrel and generally in the forward sections thereof.

Hold-down means 12 is removable, providing means for its withdrawal after the concrete has set sufficiently to maintain the predetermined spacing between the mandrel and the outer form, thus to permit concrete mix to flow, or be filled, into the spaces temporarily occupied by the downwardly projecting portions 17 of the hold-down means. The construction of the hold-down means may advantageously be in accordance with the detailed disclosure of FIGS. 7 and 8 wherein such means comprises a frame built up of channel iron members 18 and 19 suitably welded together, tubular members 17 being fixed to this frame as by welding them to gusset plates 20, 21. The lower ends 22 of tubular members 17 are advantageously disposed at an angle which generally conforms to the slope of the adjacent surfaces of the mandrel. To assist the mandrel in sliding over the hold-down means, the mandrel contacting portions 14 thereof preferably are made of such materials as nylon, Teflon or zinc babbitt, or may comprise rollers. I have found that nylon is a quite satisfactory material for mandrel contacts 14. As here illustrated the contact members 14 are formed as cylindrical plugs fitting within the tubular members 17, and are backed up by disc-shaped bearing plates 23 engaged by adjusting screws 24 threaded through nuts 25 welded to the under side of gusset plates 20. Following adjustment of the screws 24, lock nut 26 is tightened to preserve the correct adjustment. As the ends of the contact members 14- wear down, they are re-adjusted to preserve the correct spacing between the upper portions of the outer form 6 and floating mandrel 7.

The manner of attaching hold-down means 12 to the outer form 6 will be understood from FIG. 6. The upper portion of the outer form is provided with vertical flanges 27 flanking the longitudinal opening 11. To these flanges are secured, at spaced intervals lengthwise of the form, pairs of horizontally extending lugs 28 in which are formed openings spaced in accordance with the distance between openings 29 which extend vertically through the side channels 19 of the frame of the holddown means. Bolts 39 passing through the aligned openings of the frame and logs secure one or more of the hold-down means in selected positions. It will be understood that a plurality of such hold-down means are, provided at spaced intervals along the length of the form. Then, as the concrete sets sulficiently to maintain the predetermined spacing between the mandrel and outer form, successive hold-down members are withdrawn beginning at the section of the mold which has been poured first. Withdrawal of the hold-downs is easily performed by removing the bolts 30 and lifting the hold-downs with the use of a suitable chain hoist or the like engaging a hoisting tang 31 fixed to frame member 18.

The side guide means 15 includes means for withdrawal thereof and for sealing ofl. the openings in the side portions of the stationary mold surfaces of the outer form through which such guide means temporarily extended. Such withdrawal and sealing means are illustrated in FIGS. 9, l0 and 11. Side guides 15 extend through aligned apertures in upright portions of the frame 32 of the mold and outer form 6. The aperture in frame 32 may be in the form of a key slot which permits a lug 33 fixed to guide 15 to pass through the frame when lug 33 is at the three oclock position as shown in FIG. 9. After lug 33 has passed through the key slot, handle 34 of guide 15 is turned counterclockwise, bringing lug 33 to the locking position shown in FIG. to hold guide in its correct position for maintaining the proper wall thickness of the sides of the cast body. After the concrete has set sufliciently to preserve this clearance without the presence of the guides 15, handle 34 is turned back to its FIG. 9 position and the guide is completely withdrawn. Following this, concrete flows, or is filled, into the spaces formerly occupied by the guides, and the opening the wall of the outer shell 6 is sealed, or blocked, by means of a dummy 35 which is similar to guide 15, but shorter, so that when inserted in place of guide 15 with handle 34' turned into the position shown in FIG. 11, and lug 33 in its locking position, the inner surface of the dummy will just come flush with the inner surface of the outer form.

Details of the construction of the floating mandrel and outer form are shown in FIGS. 3, 4 and 5. The mandrel, FIGS. 3 and 4, is advantageously formed by a series of cylindrical sections arranged end to end, eight such sections being indicated in FIG. 1. A single section is shown in FIG. 4. It comprises a cylindrical shell 36 to each end of which is fixed an annular ring 37 provided with a series of holes 33 used to fasten the sections together. A strengthening ring 39 may be secured to the inside of the shell 36 for additional reinforcement of the shell. T-shaped members 40 are fixed to upper portions of the inside surface of the shell in positions to bring the tops of the T into supporting engagement with the shell at the points where the shell bears against the hold-down means 14 as best shown in FIG. 6. The leading end of the mandrel is provided with a plough-shaped nose 41. The upper portion of the nose section is left open as at 42 so that a blast of cooling air may be drawn through the mandrel by means of suitable blowers within the mandrel (not shown).

Details of the construction of the outer form 6 are shown in FIG. 5. It is formed with separable upper and lower parts 43, 44. Each part may comprise one or more sections bolted together end to end by means of annular attaching flanges 45 or attaching lugs 46, furnishing a series of bolt holes 47 through which bolts are passed to secure the flanges or lugs of the parts of one section of the form to corresponding flanges or lugs of the parts of an adjacent section of the form. Along the meeting edges of the parts 43 and 44 respectively are provided horizontal attaching flanges 48,- 49 having a series of aligned bolt holes 50. The upper surface of flange 49 may advantageously be made with a longitudinal groove 51 to receive a resilient packing strip 52 (FIG. 12). In the particular construction here shown, groove 51 is formed by welding a pair of flat strips 53 to the upper surface of flange 49 in spaced relation to one another. The upper and lower parts of the outer form sections may have suitable reinforcing frames or bands such as provided by the frames 54, bands and gusset plates 56, 57. Frames 54 and bands 55 are tied together across the top of opening 11 as by means of the members 58 and 59 shown in FIG. 5.

Pass-Through lacking Ring and Bulkhead Structure Another aspect of my invention is concerned with the provision of apparatus which will permit the floating mandrel to be Withdrawn at the far end of the mold while the casting operation continues and before the setting of the concrete is complete. In some forms of apparatus heretofore proposed for casting of pipe section by section, or even in a so-called continuous fashion, it is impossible to remove the mandrel or inner form until after the pipe has been removed from the casting bed. With such apparatus the inner form can be removed only with great difiiculty. This dificulty can be eliminated by the use of my apparatus wherein the means for anchoring the reinforcing members at one end of the prestressing bed comprises a frame having an open central area through which the mandrel can be withdrawn prior to relieving the prestressing tension and removal of the cast body from the outer form. This construction is illustrated in FIG. 14, which shows the mandrel 7 passing through the frame 60 of the jacking means 5. Notice that the reinforcing wires 2 are still anchored under tension by means of the cable grips 61, the wires having initially been drawn up to the desired prestressing load by means of jacks 62 (FIG. 1) hearing at one end against jack seats on abutment 4 and at the other end against jack seats associated with the jacking frame 5.

7 As applied to the continuous casting of a series of hollow bodies, my apparatus further comprises bulkhead rings disposed intermediate the ends of the outer form to divide the outer form into a plurality of mold sections, the bulkhead rings being held against lengthwise movement relative to the outer form by securing means engaging the outer form. My preferred bulkhead construction is illustrated in FIG. 13 which shows a construction in which the bulk head rings include a flexible sealing element held between a pair of ring members, this flexible sealing element being engageable by the mold surfaces of the moving mandrel 7. FIG. 13 includes the end portions of outer forms 6 arranged end to end for the continuous casting of two separate lengths of hollow piling, one of which is comprised at P1 and the other at P2. The entering bulkhead is indicated generally at 63, the exit bulkhead at 64, and the dividing bulkhead at 65. The constructions of the entering and exit bulkheads 63 and 64 are substantially the same, and include annular metal rings 66, 67 between which is disposed an annular flexible sealing element 68. I have obtained excellent results in commercial production of concrete piling with the use of the apparatus disclosed in which this flexible sealing element is made of fabric reinforced Neoprene belting in a thickness of A inch. Ring 66 of the entry bulkhead is fixed to a series of attaching lugs 69, and ring 6'7 of the exit bulkhead is secured to a series of attaching lugs '70. J-bolts 71 hooked into recesses of lugs 69 and 70 pass through the shell of outer mold sections 7 and are secured in place by nuts or other suitable means. The dividing bulkhead 65 comprises a pair of annular rings 72 with attaching lugs and J-bolts similar to those already described. A Neoprene filler 73 fills the space between the rings '22 where it is held in place by means of wire rings 74 conveniently welded to rings 72. This Neoprene filler may be slotted to receive the reinforcing wires 2.

Selective Vibratory M enns According to another aspect of my invention, the apparatus includes means for selectively applying vibratory forces to forward portions of the mandrel to produce a lubricating film of cement and Water at the mold surfaces of the mandrel and thereby assist in free continuous sliding movement of such surfaces without disturbance of the setting concrete and without pulling such surfaces of the mandrel bodily away from the concrete. This aspect of my invention will be described with particular reference to FIGS. 1, 1a, 3, 4- and 6. The vibrator mechanisms 75 used for this purpose may be of a known type conveniently driven by electric motors '76 mounted Within the mandrel. The vibrating mandrel tends to bring a surplus of cement and water to the mold sur- I? faces of the mandrel forming a film which is somewhat slippery. Also, because this film contains an excess of water, it does not set as fast as the parent concrete mix from which it came. I have found that if the vibrators are properly placed inside the mandrel, the mandrel becomes self-lubricating and that the lubricating film of cement and water wiil not harden until sometime after the concrete mix has hardened. Thus with proper control of speed of the mandrel, the lubricating film remains liquid throughout the length of the mandrel but the base concrete hardens before the end of the mandrel clears it.

I have found further that it is particularly advantageous to secure the vibrators to inner portions of the mandrel in positions which are selectively varied circumferentially of the mandrel depending upon their respective distances from the leading end of the mandrel. This arrangement will now be described with reference to FIG. 1. If we consider that the mandrel 7 is made up of a series of sections arranged end to end in the manner already described, it will be observed that, as shown in this view, the mandrel comprises eight of such sections. Beginniru with the section which is to the right of FIG. 1 and which constitutes the leading end of the mandrel, as section No. 1, and numbering from right to left, the arrangement of the vibrators is as follows: The pair of horizontally opposed vibrators 77 in the rear portion of section No. 1 are mounted low to compact the concrete in the bottom portion of the pipe. The pair of vibrators 78, S in the forward parts of sections No. 2 and No. 3 are mounted high and are for the purpose of causing concrete dumped into the top to flow down through the sides of the mandrel. (In the vicinity of section No. 2, the form is not filled to the top with concrete.) The pair of vibrators 79 in the rear of section No. 2 are to compact the concrete. Since the form is filled to a higher level here than at section No. 1, these vibrators are located slightly higher than those in section No. 1. In the forward part of section No. 3, we have a pair of horizontally opposed vibrators 80 which again are mounted high, and at the rear of section No. 3 the pair of vibrators 81 are mounted at a higher point than the vibrators '79 at the rear of section No. 2. Finally in section No. 4-, the vibrators 82; and 83 are all mounted near the top. In particular it will be observed with reference to the vibrators located in the rear part of the several sections, that each pair is mounted at a higher point than those of the preceding section. Thus vibrators 79 are higher than vibrators 7'7, vibrators 8 higher than vibrators '79, and vibrators 83- higher than vibrators 31. At section No. 4, the form is completely filled with concrete, and the vibrators in the top of section No. 4 compact the top part of the pile.

Thus according to the vibrator arrangement I have described, the selective vibrator positions include positions which are in a lower sector of the mandre nearest the leading end thereof and in progressively higher sectors as their distances from the leading end increase. I prefer that the selective vibrator positions include other positions (those of vibrators 78, St and 82) in upper sectors of the mandrel at locations intermediate the positions located in said progressively high-er sectors i.e. intermediate the positions occupied by vibrators '77, 79, 81 and S3.

The vibrators are operated at a speed between 6000 and 7000 r.p.m. The nature frequency of the fourth mode of vibration of the mandrel as a free beam should fall within this range. One pair of vibrators, located near a point of maximum amplitude of this mode, will have their speed adjusted slightly to correspond to this natural frequency, which will have to be determined by experiment after the mandrel is assembled. Thus, a small amount of vibration will be transmitted through the entire mandrel. It is desirable to have some vibration through the entire mandrel, to help in reducing friction,

u but the amount of vibration in the rear end should be kept small.

Another advantageous feature of my preferred form of apparatus is illustrated in FIGS. 2 and 3 in which I have shown a boom 84 formed by tubular members or rods projecting forwardly from the mandrel. This boom supports, or includes, a battery of electrical controls 85 movable in a trajectory which makes the controls accessible for actuation through the lengthwise opening 11 in the upper part of the outer form. With this arrangement any one or more of the several vibrators or pairs of vibrators can be turned on and off as may be needed for best control of the vibratory action as the casting operation proceeds. Notice that the controls 35 are mounted on the boom at a location spaced a substantial distance in front of the leading end of the mandrel so that concrete mix can be dropped through the opening 11 at points between the controls and the leading end of the mandrel without entering the mandrel ventilating opening 42 (FIG. 3) previously described. It may be mentioned here that the cable purchase 9 is secured to the leading end of the mandrel by a suitable length of towing cable 86 whereby the block 37 at the end of the purchase can be located forwardly of the concrete dropped into the form ahead of the nose of the mandrel.

The cast product is illustrated in FIG. 15 which shows the arrangement of pretension strands 2 and spiral hooping 89. Here we see a representation of a commercial piling in which the first few turns of the spiral hooping are closer together as represented at the left-hand end of FIG. 15. For example, there might be five turns at /4 inch pitch (from A to 13) followed by 60 turns at 2 inch pitch for a distance of 10 feet (from B to C) followed in turn by a 4 inch maximum pitch extending to the mid-point of the length of the pile, the construction of the complete pile being symmetrical about such mid point. If desired the end of the pipe may be reinforced by a bar ring 90 as shown in FIG. 15 from which extends a series of circumferentially spaced L-shaped bar prongs 91.

The winch 8 is located a sufficient distance beyond the jacking means 5 to permit the mandrel to be fully withdrawn from the form. The winch is driven by a variable speed motor and the winch mechanism is rigged in such a way that the whole mechanism will overturn before a load sufiicient to break the winch or cable is reached. A dynamometer is used, so that the pulling tension is known at all times. Piling such as sections 54 inches in diameter, in lengths averaging around feet, is quite typical of members suitable to be made with the use of my apparatus. It will be understood, however, that other members such as hollow box beams, would be equally suitable for manufacture with this apparatus. The piles are currently manufactured two or three at a time on a 264 casting line, depending upon the length of the pile. The mandrel will be moved about one foot per minute, thus taking between 4 and 5 hours to pour a line. After pouring, the ends of the line are closed with discs of Styrofoam, and the heat released from hydration of the concrete is retained inside of the pile, facilitatiing curing. In 16 to 24 hours, the extremely dry mix used (zero slump) will have hardened to the 5000 psi. strength necessary for release of the pretensioning. The top half of the outer form is then lifted, and the tendons cut off at the end of each pile. After removal of the piles, the intermediate and end bulkhead rings are positioned for the next pour, and tendons are stretched through the dividing bulkheads and through coils of spiral. After jacking the tendons, the spiral is then spread out along the length of the pile, and tied in position to the tendons. The top half of the form is replaced, guides are inserted, and the mandrel is positioned behind the line at one end, ready for pouring. The entire cycle is normally about 36 hours, although it can be as little as 24 hours.

Approximate Outside Outside Diameter Mandrel Section N 0. Diameter as After Fabricated, Finish Inches Grinding,

Iinches Notice that the variation in finished diameter throughout the 64 ft. length of this mandrel is less than one-tenth of one inch. This difference in diameter is only enough to relieve the elastic strain in the mandrel gradually, and to compensate for a slight shrinkage of the concrete during initial set. Thus the mandrel does not draw away from the concrete as it moves forward. As a result, the cast pile will be of uniform inside diameter throughout its length. If a tapered mandrel of the type designed for step-by-step, or batch, operation were to be used for continuous operation, the degree of taper would be such as to allow the concrete to settle slightly near the small end, disturbing the concrete during initial set, and causing internal flaws in the concrete. This difficulty is not experienced with my substantially uniform mandrel surface when constructed and operated in the manner which I have described, with emphasis on the advantages obtained with the use of my floating mandrel structure, selective vibratory means, and-as applied to the production of hollow prestressed bodies-the use of one or both of such features in conjunction with the pass-throng jacking ring and bulkhead structure.

The terms and expressions which I have employed are used in a descriptive and not a limiting sense, and I have no intention of excluding equivalents of the invention described and claimed.

I claim:

1. Apparatus for continuous casting of hollow concrete bodies comprising a horizontal outer form having stationary mold surfaces adapted to form substantially the complete exterior of the body and having a substantially continuous opening extending lengthwise along an upper portion thereof, a mandrel completing a mold cavity with the outer form, said mandrel movable lengthwise through the outer form and having mold surfaces adapted to form the interior of the body while the mandrel is in continuous movement through the outer form, means for producing such continuous movement of the mandrel, means for introducing the concrete mix through an upper portion of the outer form during such continuous movement of the mandrel, and stationary hold-down means projecting downwardly below upper portions of the stationary mold surfaces of the outer form in positions spaced along the length of the outer form and within the mold cavity and arranged for guiding engagement with upper portions of the mold surfaces of the moving mandrel, the mandrel being free to float under hydrostatic pressure of the concrete mix to maintain guiding contact with said holddown means until the concrete has set sufficiently to maintain a predetermined spacing between the mandrel and outer form in accordance with the predetermined position of the mandrel-engaging portions of the hold-down means.

2. Apparatus according to claim 1, which includes of the stationary mold surfaces of the outer form.

3. Apparatus according to claim 2, which includes means for withdrawing said guide means and sealing off the openings in the side portions of the stationary mold surfaces of the outer form through which said guide means temporarily extended.

4. Apparatus according to claim 5, which includes means located in forward portions of the mandrel for selectively applying vibratory forces to forward portions of the mandrel to produce a lubricating film of cement and water at the mold surfaces of the mandrel and thereby assist in free continuous sliding movement of such surfaces without disturbance of the setting concrete and without pulling such surfaces of the mandrel bodily away from the concrete.

5. Apparatus according to claim 1, which includes ballasting means located in the lower part of the mandrel to maintain an upright position of the floating mandrel thereby to prevent rotation of the mandrel during its continuous movement through the outer form.

6. Apparatus according to claim 1, in which said holddown means are arranged to be withdrawn after the concrete has set sufficiently to maintain said predetermined spacing between the mandrel and outer form, thus to permit concrete mix to completely fill the spaces temporarily occupied by the hold-down means.

7. Apparatus according to claim 1, which includes means located in forward portions of the mandrel for selectively applying vibratory forces to forward portions of the mandrel to produce a lubricating film of cement and water at the mold surfaces of the mandrel and thereby assist in free continuous sliding movement of such surfaces without disturbance of the setting concrete and without pulling such surfaces of the mandrel bodily away from the concrete.

8. Apparatus according to claim 1, which includes guide means projecting inwardly through side portions of the stationary mold surfaces of the outer form, and ballasting means to maintain an upright position of the floating mandrel thereby to prevent rotation of the mandrel during its continuous movement through the outer form.

9. Apparatus according to claim 1, which includes guide means projecting inwardly through side portions of the stationary mold surfaces of the outer form, and in which said hold-down means are arranged to be withdrawn after the concrete has set sufficiently to maintain said predetermined spacing between the mandrel and outer form, thus to permit concrete mix to completely fill the spaces temporarily occupied by the hold-down means.

10. Apparatus according to claim 1, which includes ballasting means located in the lower part of the mandrel to maintain an upright position of the floating mandrel thereby to prevent rotation of the mandrel during its continuous movement through the outer form, and means located in forward portions of the mandrel for selectively applying vibratory forces to forward portions of the mandrel to produce a lubricating film of cement and water at the mold surfaces of the mandrel and thereby assist in free continuous sliding movement of such surfaces without disturbance of the setting concrete and without pulling such surfaces of the mandrel bodily away from the concrete.

11. Apparatus for continuous casting of hollow reinforced concrete bodies comprising a horizontal prestressing bed, means for anchoring reinforcing members to the ends of the bed in positions to extend through wall portions of the cast body, a horizontal outer form having stationary mold surfaces adapted to form substantially the complete exterior of the body, a mandrel movable lengthwise through the outer form and having mold surfaces adapted to form the interior of the body while the continuous movement of the mandrel, means associated with the outer form for guiding engagement with mold surfaces of the moving mandrel, and means located in forward portions of the mandrel for selectively applying vibratory forces to forward portions of the mandrel to produce a lubricating film of cement and water at the mold surfaces of the mandrel and thereby assist in free continuous sliding movement of such surfaces without disturbance of the setting concrete and without pulling such surfaces of the mandrel bodily away from the concrete.

12. Apparatus according to claim 11 in which said means for applying vibratory forces comprise vibrators secured to inner portions of the mandrel in positions which are selectively varied circumferentially of the mandrel depending upon their respective distances from the leading end of the mandrel.

13. Apparatus according to claim 12 in which said selective vibrator positions include positions which are in a lower sector of the mandrel nearest the leading end thereof and in progressively higher sectors as their distances from the leading end increase.

14. Apparatus according to claim 12 in which said selective vibrator positions include positions which are in a lower sector of the mandrel nearest the leading end thereof and in progressively higher sectors as their distances from the leading end increase and further include other positions in upper sectors of the mandrel at locations intermediate the positions located in said progressively higher sectors.

15. Apparatus according to claim 11 in which the means for introducing the concrete mix includes a substantially continuous opening extending lengthwise along an upper portion of the outer form, and in which a boom projects forwardly from the mandrel, said boom including controls for the respective vibrator means, such controls being movable with the mandrel in a trajectory which makes the controls accessible for actuation through said lengthwise opening.

16. Apparatus according to claim 15 in which said controls are mounted on said boom at a location spaced a substantial distance in front of the leading end of the mandrel whereby concrete mix can be dropped through said opening at points between the controls and the leading end of the mandrel without entering a mandrel-ventilating opening in said leading end.

References Cited in the file of this patent UNTTED STATES PATENTS 977,345 Tidnam Nov. 29, 1910 1,146,263 Keller July 13, 1915 1,204,936 Camp Nov. 14, 1916 1,888,101 Wilson Nov. 15, 1932 1,911,163 Prowant May 23, 1933 2,299,111 Rogers Oct. 20, 1942 2,356,852 Hutchinson Aug. 29, 1944 2,948,042 Sylvester Aug. 9, 1960 2,968,082 Schatze et a1. Jan. 17, 1961 2,987,793 Martin June 13, 1961 3,047,928 Carr Aug. 7, 1962 FOREIGN PATENTS 565,139 Canada Oct. 28, 1958 

1. APPARATUS FOR CONTINOUS CASTING OF HOLLOW CONCRETE BODIES COMPRISING A HORIZONTAL OUTER FORM HAVING STATIONARY MOLD SURFACES ADAPTED TO FORM SUBSTANTIALLY THE COMPLETE EXTERIOR OF THE BODY AND HAVING A SUBSTANTIALLY CONTINOUS OPENING EXTENDING LENGTHWISE ALONG AN UPPER PORTION THEREOF, A MANDREL COMPLETING A MOLD CAVITY WITH THE OUTER FORM, SAID MANDREL MOVABLE LENGTHWISE THROUGH THE OUTER FORM AND HAVING MOLD SURFACES ADAPTED TO FORM THE INTERIOR OF THE BODY WHILE THE MANDREL IS IN CONTINOUS MOVEMENT THROUGH THE OUTER FORM, MEANS FOR PRODUCING SUCH CONTINUOUS MOVEMENT OF THE MANDREL, MEANS FOR INTRODUCING THE CONCRETE MIX THROUGH AN UPPER PORTION OF THE OUTER FORM DURING SUCH CONTINOUS MOVEMENT OF THE MANDREL, AND STATIONARY HOLD-DOWN MEANS PROJECTING DOWNWARDLY BELOW UPPER PORTIONS OF THE STATIONARY MOLD SURFACES OF THE OUTER FORM IN POSITIONS SPACED ALONG THE LENGTH OF THE OUTER FORM AND WITHIN THE MOLD CAVITY AND ARRANGED FOR GUIDING ENGAGEMENT WITH UPPER PORTIONS OF THE MOLD SURFACES OF THE MOVING MANDREL, THE MANDREL BEING FREE TO FLOAT UNDER HYDROSTATIC PRESSURE OF THE CONCRETE MIX TO MAINTAIN GUIDING CONTACT WITH SAID HOLDDOWN MEANS UNTIL THE CONCRETE HAS SET SUFFICIENTLY TO MAINTAIN A PREDETERMINED SPACING BETWEEN THE MANDREL AND OUTER FORM IN ACCORDANCE WITH THE PREDETERMINED POSITION OF THE MANDREL-ENGAGING PORTIONS OF THE HOLD-DOWN MEANS. 